Recipe 19.2 Redirecting Error Messages

19.2.1 Problem

19.2.2 Solution

Use the CGI::Carp module from the standard Perl distribution to
prefix each line on STDERR with the program name
and current date. You can also send warnings and errors to a file or
the browser if you wish.

19.2.3 Discussion

Tracking down error messages from CGI scripts is notoriously
annoying. Even if you manage to find the server error log, you still
can't determine which message came from which script, or at what
time. Some unfriendly web servers even abort the script if it has the
audacity to emit anything out its STDERR before
the Content-Type header is generated on
STDOUT, so warnings can get you into trouble.

Enter the CGI::Carp module. It replaces warn and
dieplus the normal Carp module's
carp, croak,
cluck, and confess
functionswith more verbose and safer versions. It still sends
them to the normal server error log.

use CGI::Carp;
warn "This is a complaint";
die "But this one is serious";

The following use of CGI::Carp also redirects errors to a file of
your choice, placed in a BEGIN block to catch compile-time warnings
as well:

You can even arrange for fatal errors to show up at the client
browser, which is nice for your own debugging but might confuse the
end user.

use CGI::Carp qw(fatalsToBrowser);
die "Bad error here";

Even if the error happens before you get the HTTP header out, the
module will try to detect this and avoid the dreaded
500ServerError. Normal warnings still go to the server
error log (or wherever you've sent them with
carpout) with the program name and date stamp
prepended.

19.2.4 See Also

The documentation for the standard CGI::Carp module; the discussion
on BEGIN in Recipe 12.3